Fire up Google today and you'll be greeted by the Google logo as a lush forest - the web giant's nod to and celebration of the 40th anniversary of Earth Day. This so-called Google Doodle appears to depict a collection of six parrots, which I'm taking - Google doesn't provide explanatory gallery notes - to be a reference to the fact that 2010 is also the International Year of Biodiversity, to be marked on 22 May.

This isn't the first time Google has given over its logo for Earth Day. Last year, it ran an illustration of a waterfall and a rainbow of marine life (quite cool), in 2008 it plumped for the logo as a pile of rocks with vegetation growing on it (slightly random), and in 2007 depicted the Google logo as melting polar ice (very apt seeing as the loss of Arctic ice that summer left experts "stunned").

Beyond the natural world, it has also previously celebrated Earth Day by taking a look at the solutions to some of our environmental problems: 2006 featured solar panels atop the famous logo with a wind turbine in the background.

Earth Day, of course, is a bit older than Google, with the first taking place in the US in 1970, thanks to Gaylord Nelson, a US senator and Democrat, who died in 2005. In the words of its organisers, it is designed to "[activate] individuals and organizations to strengthen the collective fight against man's exploitive relationship with the planet." No mean feat then. It's very much a product of the burgeoning environment movement of its time, and a clear forerunner to modern green coalitions, such as TckTckTck for the ongoing international climate talks, Ask The Climate Question for the election, along with countless other groups and invididuals.

Robert Stone, a film-maker who recently released a documentary called Earth Days on the genesis of the environment movement and the founding of Earth Day, seems to think the "day" has done its job. He told the New York Time's Andy Revkin this week:

"The environmental movement in the late 60s and early 70s was driven by a strong sense of urgency that I think you see conveyed in the footage of those times. The movement now is sort of a victim of its own success in that our environment as a whole seems pretty good."